1. Field of the Invention
The present invention relates to radio transmission, and more particularly to a keying device for adding an audio signal at the end of a normal transmission.
2. Description of the Prior Art
It is common in two-way radio transmissions to add an additional audio signal when an information bearing transmission completed. Such audio signals alert the receiving party that the transmission is ended, and the receiving party may respond. Some transmission systems are supplied with internal circuitry that provides this function. However, a variety of two-way radio systems do not provide this function.
For example, radio operators often desire to add a novel sound burst, distinctive of the operator, when a transmission is completed. Thus, there is a need for a device that may be connected to existing transmitters to sense the end of a transmission, re-key the transmitter, and modulate the radio signal with a sound signal.